1. Field of the Invention
The present invention relates to a flexible printed circuit and a method of manufacturing the same, and more particularly, to a double-sided flexible printed circuit which can be used as a signal transfer route in a compact hard disk drive, and a method of manufacturing the same.
2. Description of Related Art
Hard disk drives (HDDs) are information storage devices for personal computers. With the continuous miniaturization of HDDs, they are increasingly used as information storage devices for portable electronic devices such as mobile phones or MP3 players.
FIG. 1 is a perspective view of a conventional compact HDD. Referring to FIG. 1, a conventional compact HDD 10 includes a base member 11 and a cover member 12 coupled to the base member 11. A spindle motor 15 to rotate a disk 13 and an actuator 17 to move a magnetic head (not shown) to a desired position on the disk 13 are installed on the base member 11.
The actuator 17 includes a swing arm 18 rotatably coupled to the base member 11 and a suspension 19 installed at one end portion of the swing arm 18 and supporting a head slider 20 with the magnetic head mounted thereon to be elastically biased toward the surface of the disk 13. The actuator 17 has a voice coil motor (VCM) 22 to rotate the swing arm 18. The voice coil motor 22 includes a VCM coil 23 coupled to the other end portion of the swing arm 18 and a magnet 24 installed on the base member 11 to face the VCM coil 23. The voice coil motor 22 is controlled by a servo control system and rotates the swing arm 18 in a direction according to the Fleming's left hand rule by the interaction of current input to the VCM coil 23 and a magnetic field formed by the magnet 24.
A printed circuit board (not shown) is arranged on the bottom surface of the base member 11. Semiconductor chips and other circuit devices (not shown) to operate the actuator 17, the magnetic head, and spindle motor 15 are mounted on the printed circuit board. The printed circuit board and the actuator 17 are connected by a flexible printed circuit 30.
FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1. Referring to FIG. 2, the flexible printed circuit 30 includes a conductive layer 35 formed of copper (Cu) into a circuit pattern and provided between first and second insulation layers 31 and 32 formed of polyimide. The conductive layer 35 is attached to the first insulation layer 31 via an adhesive layer 36 and the second insulation layer 32 is attached to the conductive layer 35 and the first insulation layer 31 via another adhesive layer 37.
The conventional flexible printed circuit 30 has a problem in that, as the first and second insulation layers 31 and 32 are formed of a polyimide film exhibiting a relatively large stiffness, a large amount of electric power is needed for the rotation of the actuator 17 because the stiffness of the flexible printed circuit 30 increases. Also, since the viscosity of the first and second adhesive layers 36 and 37 changes greatly according to a change in temperature, the stiffness of the flexible printed circuit 30 changes greatly according to the change in temperature. As a result, the rotation control of the actuator 17 becomes difficult so that information processing speed of the hard disk drive 10 decreases.
A plurality of circuit patterns are formed on the conductive layer 35 of the flexible printed circuit 30. A width Wp of each circuit pattern and a gap G between adjacent circuit patterns must be maintained over tens of micrometers to secure the reliability in signal transfer. Accordingly, the width Wa of the entire flexible printed circuit 30 increases so that miniaturization of the compact HDD 10 is difficult.